/afs/cern.ch/work/a/aaltunda/public/www/CMSSW_6_2_7/src/RecoPixelVertexing/PixelTriplets/plugins/ThirdHitPredictionFromInvLine.cc

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#include "ThirdHitPredictionFromInvLine.h"

#include <cmath>
#include "DataFormats/GeometryVector/interface/GlobalVector.h"
#include "DataFormats/GeometryVector/interface/GlobalPoint.h"

#include "RecoTracker/TkMSParametrization/interface/PixelRecoUtilities.h"
#include "RecoTracker/TkMSParametrization/interface/PixelRecoRange.h"

template <class T> T sqr( T t) {return t*t;}

typedef Basic3DVector<double> Point3D;
typedef Basic2DVector<double> Point2D;
typedef PixelRecoRange<double> Ranged;

#include <iostream>

using namespace std;

ThirdHitPredictionFromInvLine::ThirdHitPredictionFromInvLine(
    const GlobalPoint & P1, const GlobalPoint & P2,
    double errorRPhiP1, double errorRPhiP2)
    : nPoints(0), theSum(0.),  theSumU(0.), theSumUU(0.), theSumV(0.), theSumUV(0.), theSumVV(0.),
      hasParameters(false),  theCurvatureValue(0.), theCurvatureError(0.), theChi2(0.)
{
  GlobalVector aX = GlobalVector( P1.x(), P1.y(), 0.).unit();
  GlobalVector aY( -aX.y(), aX.x(), 0.);
  GlobalVector aZ( 0., 0., 1.);
  theRotation = Rotation(aX,aY,aZ);

  add(P1, errorRPhiP1);
  add(P2, errorRPhiP2);

}

GlobalPoint ThirdHitPredictionFromInvLine::crossing(double radius) const
{
  double A = -(theSum*theSumUV-theSumU*theSumV)/(sqr(theSumU)-theSum*theSumUU);
  double B = (theSumU*theSumUV - theSumUU*theSumV)/(sqr(theSumU)-theSum*theSumUU);
  double delta =  sqr(2.*A*B) - 4*(1+sqr(A))*(sqr(B)-sqr(1/radius));
  double sqrtdelta = (delta > 0.) ? sqrt(delta) : 0.; 
  double u1 = (-2.*A*B + sqrtdelta)/2./(1+sqr(A)); 
  double v1 = A*u1+B;
  Point2D tmp = PointUV(u1,v1, &theRotation).unmap();
  return GlobalPoint(tmp.x(), tmp.y(), 0.);
}


void ThirdHitPredictionFromInvLine::add(const GlobalPoint &p, double errorRPhi)
{
  double weigth = sqr(sqr(p.perp())/errorRPhi);
  add(PointUV(Point2D(p.x(),p.y()), &theRotation), weigth);
}

void ThirdHitPredictionFromInvLine::add(const ThirdHitPredictionFromInvLine::PointUV & point, double weigth)
{
  hasParameters = false;
  nPoints++;
  theSum += weigth;
  theSumU += point.u()*weigth;
  theSumUU += sqr(point.u())*weigth;
  theSumV += point.v()*weigth;
  theSumUV +=  point.u()*point.v()*weigth; 
  theSumVV += sqr(point.v())*weigth;
}

void ThirdHitPredictionFromInvLine::remove(const GlobalPoint &p, double errorRPhi)
{
  hasParameters = false;
  PointUV point(Point2D(p.x(),p.y()), &theRotation);
  double weigth = sqr(sqr(p.perp())/errorRPhi);
  nPoints--;
  theSum -= weigth;
  theSumU -= point.u()*weigth;
  theSumUU -= sqr(point.u())*weigth;
  theSumV -= point.v()*weigth;
  theSumUV -=  point.u()*point.v()*weigth;
  theSumVV -= sqr(point.v())*weigth;
}

void ThirdHitPredictionFromInvLine::print() const
{
  std::cout <<" nPoints: " << nPoints <<" theSumU: "<< theSumU <<" theSumUU: "<<theSumUU
                                      <<" theSumV: "<< theSumV <<" theSumUV: "<<theSumUV<<std::endl;
}

void ThirdHitPredictionFromInvLine::check() const
{
  if (hasParameters) return;

  long double D = theSumUU*theSum - theSumU*theSumU;
  long double A = (theSumUV*theSum-theSumU*theSumV)/D;
  long double B = (theSumUU*theSumV-theSumUV*theSumU)/D;
  double rho =  2.*fabs(B)/sqrt(1+sqr(A));
  double sigmaA2 = theSum/D;
  double sigmaB2 = theSumUU/D;

  hasParameters = true;
  theCurvatureError = sqrt( sqr(rho/B)*sigmaB2+ sqr(rho/(1+sqr(A)))*sigmaA2); 
  theCurvatureValue = 2.*fabs(B)/sqrt(1+sqr(A)); 
  theChi2 = theSumVV - 2*A*theSumUV - 2*B*theSumV + 2*A*B*theSumU + B*B*theSum + A*A*theSumUU;
}

/*
GlobalPoint ThirdHitPredictionFromInvLine::center() const
{
  long double den = theSumU*theSumUV - theSumUU*theSumV; 
  double a = (theSum*theSumUV-theSumU*theSumV)/2./den;
  double b = (sqr(theSumU)-theSum*theSumUU)/2./den;
  Point3D tmp = theRotation.multiplyInverse( Point2D(a,b) );
  return GlobalPoint(tmp.x(), tmp.y(), 0.);
}
*/